Note for GMs: The following item has been made intentionally stronger, this is because in its original printing the author put a high value on the challenges that were required to attain it. Caution is advised when granting it to player characters.
Spirit Knife
Weapon (dagger), very rare (requires attunement)
The spirit knife is capable of brief surges of tremendous destructive power, breaking down objects, armor, and flesh with ease. It seems to flicker in and out of existence, only fully materializing right before a strike.
You gain a +2 bonus to attack and damage rolls made with this magic weapon. When you hit with this weapon, you can cast disintegrate as a bonus action targeting the creature or object you just hit. If the target is an object, it takes maximum damage from disintegrate. If the target is a creature, it has disadvantage on its saving throw against the spell. Once used, you cannot use this property again until the next dawn.
Ref: T&H p165